By Dragos Micu and Valentina Todorova
During the summer of 2007 a Bulgarian-Romanian diving team of marine
biologists carried out a series of expeditions along the Western Black Sea coast
with the main goal of identifying sites suitable for designation as Marine
Protected Areas. We found more than we expected, including discoveries that
went far beyond the initial scope of our project and which we feel deserve a
broader audience.
A newly-discovered
unique habitat
© Dragos Micu
We were diving along the rocky shores of the
Southern Bulgarian coast, searching for live
oysters to verify their occurrence. To our
surprise, we came across Ostrea edulis biogenic
reefs, a new type of habitat and unique to
European seas – and probably the world.
Unlike other European biogenic reefs,
dominated by tube-building polychaetes such
as Sabellaria (Porras et al., 1996; Gruet, 1985;
Moore, 1996), Serpula vermicularis (Earll, 1992;
Bosence, 1973), Ficopomatus enigmaticus (Micu
& Micu, 2004) or mussels like Mytilus
(Gosling, 1992) and Modiolus (Magorrian et
al., 1995), the ostrak is built almost exclusively
by the flat oyster, Ostrea edulis. Small serpulid
polychaetes do occur on the ostrak also, but, if
we imagine ostrak as a fortress wall, then the
oysters are the stones and the polychaetes are
the cement – a very thin one, that is.
Unlike the oyster beds commonly known from
the intertidal of Western Europe and North
America – 7m in height, 30-50m in length and
10m in width for each mound – Black Sea
ostrak are massive, towering biogenic
structures, dwarfing the human observer.
(a). Flat oyster (Ostrea edulis) biogenic reef.
“Ostrak” is what these reefs are called by
local fishermen. They think the name
comes from the Bulgarian word “ostar,”
meaning sharp, and associate it with the
edges of oyster shells sticking out from
the reef, sharp enough to cut the hands
or the neoprene suit of a careless diver.
However, in the authors’ opinion the name
originates from “Ostrakon,” meaning
oyster shell, and was probably given to
the oyster reefs by the ancient Greeks
who first witnessed their existence
thousands of years ago.
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MarBEF Newsletter
Autumn 2007
Unlike the small, estuarine oyster reefs built by
Crassostrea virginica on the south-eastern US
coast (Posey et al., 2003; Grizzle et al., 2002),
ostrak reefs occur in clear marine waters with
no freshwater input, forming a belt between 7
and 23m in depth, parallel to rocky coasts.
Smaller ostrak formations may also occur on
rocky offshore reefs or as a sponge-like
structure adhering to rocky vertical drop-off
faces.
Local people have pointed out many locations
where ostrak is present but, due to the limited
time and resources, we were only able to dive
briefly at three sites. These reefs were
overgrown by sponges, mussels (Mytilus
galloprovincialis) and algae (Delesseria ruscifolia
and Zanardinia prototypus) and harboured a
very diverse marine life. While fresh oyster
shells were visible on the reefs, no live oysters
were recorded at these sites (see photo b).
Only a few years ago, local people collected
live oysters from these very reefs and there are
many more sites at which we could not dive, so
we are hopeful that other oyster reefs in the
© Dragos Micu
Biodiversity of the Western Black Sea
(b). Ostrea edulis reef with no live oysters.
area may still be alive.
Our discoveries have raised some questions:
1. Do live reefs still exist? We are currently
trying to find funding to carry out more
extensive field research which will allow us to
map all the sites where ostrak habitat occurs.
During this search, we hope to discover some
live oyster reefs.
2. Why did the oysters perish at the sites
investigated by us? The oysters were never
commercially fished, and recreational harvest
was very limited, so overfishing can be ruled
out as a cause of extinction. Were oysters killed
by eutrophication and diseases brought with
cultured Crassostrea gigas in the Russian part
of the Black Sea? Were they decimated by the
alien predatory whelk Rapana venosa? More
research is needed to find out.
3. Is oyster reef restoration possible? The
idea of restoring the amazing Ostrak reef
ecosystem came to us as soon as we
discovered the reefs, but it is very clear that
any attempt at reintroduction is futile while we
don’t understand the reasons/causes behind
the oyster reefs die-out in the first place.
Rare species
We encountered a number of rare species
during our dives – among them, the PontoCaspian relicts Neogobius kessleri and
large, older whelks attacking one of the many
juveniles around them, but also with several
juveniles attacking together a larger whelk,
weakened by starvation.
© Dragos Micu
Syngnathus abaster, both found in the Veleka
River estuary. This is a new distribution record
for Neogobius kessleri, previously known only
from the Danube, Danube Delta, Dniester and
adjacent lakes (Banarescu, 1964; Jivkov &
Karapetkova, 2007).
This Rapana superinvasion changes the reef
ecosystem drastically and is bound to interfere
with the lives of other species inhabiting the
reef. The onset of starvation affects not only
Rapanas but all of the other species of
invertebrates and demersal fishes which
depend on mussels as their staple food. Those
which are mobile enough, like the fishes, will
leave the reef for better pastures, while those
which are less mobile, like crabs, will starve and
eventually die, only to be consumed by the
whelks. This leads to a massive loss of
biodiversity and impaired reef ecosystem
functioning.
Other Mediterranean fishes, rare in the Black
Sea, were Chromis chromis, Diplodus annularis,
Gobius
bucchichi,
Gobius
paganellus,
Zosterisessor ophiocephalus, Arnoglossus kessleri,
Uranoscopus scaber, Gobius cobitis, Salaria pavo,
Blennius ocellatus, Coryphoblennius galerita,
Aphia minuta and Nerophis ophidion.
We found several bivalve molluscs which are
rare for the Black Sea (Dumont, 1999; Micu,
2004): Loripes lacteus in fine sands, Petricola
lithophaga in sandstone, Teredo navalis in
wooden debris and Pholas dactylus in marl, the
latter species listed in the Bern and Barcelona
Conventions (Micu, 2007; SoHelME, 2005).
Few species can cope with the new conditions,
but some do. Until now, there have been very
few natural enemies of Rapana known from the
areas it has invaded around the globe. In the
Chesapeakes, blue crabs Callinectes sapidus
consumed Rapana in laboratory experiments,
but it is not known if they do so in nature
(Harding, 2003). Seastars eat Rapana in and
around the Bosphorus (Zaitsev & Ozturk,
2001), but they do not live in the Black Sea
proper.
Rare crustaceans (Dumont, 1999; Micu &
Micu, 2006) which we found included the
barnacle Chthamalus stellatus, the endemic
mysids Hemimysis sp, the thalassinid Pestarella
candida, the crab Polybius navigator and the
hermit crab Clibanarius erythropus.
Climate change-induced
phenomena in the Western
Black Sea
The Black Sea has, by and large, two climate
types: submediterranean on the eastern and
southern coasts, and Crimean and temperate
on the western and northern coasts. The
temperate climate on the western coasts has
provided, until now, suboptimal conditions for
the development of the alien predatory
gastropod Rapana venosa, which originates
from the warmer Asian seas (Sea of Japan to
Hong Kong). Although a common and well
adapted species, Rapana has never caused
local extinction or generalised stock depletion
of its bivalve prey species on the western
coast. We could say that its invasiveness has
proven to be only mild to medium here, and
with the onset of commercial fisheries for it in
the 1980s, Rapana became more a resource
than a threat.
We
have
heard
through
personal
communications, as well as reading in Russian
scientific papers, about the occurrence of
massive settlements of the alien predatory
(c). Rapana settlement.
gastropod Rapana venosa in the Eastern Black
Sea (Chikina & Kucheruk, 2005). These cyclic
events lead to high densities of young Rapana,
which wipe out all prey items available in the
area before dying off of starvation, which in
turn leads to the onset of impoverished and
dysfunctional ecosystems. For us who, for
decades, lived “peacefully” on the western
coast, with Rapana well-integrated in our
marine ecosystems and a major cash crop for
our commercial fisheries, these accounts, even
when properly illustrated, were hard to believe.
Well, not anymore!
In 2006 and 2007, massive settlement of
Rapana juveniles occurred at many sites along
the Bulgarian coast. Shallow rocky shores and
offshore reefs seem to be the preferred sites
for such events. We have witnessed and
documented incredible densities, with the
substrate completely covered with a compact
blanket of Rapana juveniles of the 0+ to 1+
year-classes. The bivalve populations of the
area are completely obliterated, even the
smallest species, such as Mytilaster lineatus.
The whelks then resort to scavenging,
consuming all corpses available in the area:
fishes, crabs and even seabirds (see photo c).
As a last resort, we have observed for the first
time cannibalism among Rapa whelks, with
On the Bulgarian coast, we have documented
for the first time the consumption of Rapana
by a native species in the wild. The robust crab
Eriphia verrucosa is strong enough to crush the
shells of juvenile Rapana and eat them. This is
probably why densities of the crab seem
unchanged on the reefs affected by the Rapana
superinvasion (see photo d).
© Dragos Micu
Phyllophora nervosa, Delesseria ruscifolia,
Laurencia sp and Zanardinia prototypus should
be pointed out as rare algae (Dumont, 1999;
Dimitrova-Konaklieva S, 2000) that we found
along the Bulgarian coast.
(d). Robust crab (Eriphia verrucosa).
Autumn 2007
MarBEF Newsletter
27
© Dragos Micu
sites. Its only available record from the Black
Sea until now refers to the Bosphorus Strait
inside Istanbul city (Hureau, 1991). The red
mullet’s spread to the north is another clear
indication of the Black Sea’s accelerated
mediterranisation, associated with global
climate change (see photo e).
Further evidence was provided by the
supralittoral association of the barnacle
Chthamalus stellatus and the snail Melaraphe
neritoides, whose northern limit used to be at
cape Kaliakra but which has extended around
30km northwards to Tyulenovo village.
Acknowledgments
These studies were carried out within the
framework of the project “Marine Protected
Areas in Bulgaria & Romania,” supported by
the BBI-Matra Action Plan Support Scheme
2005-’08 of the Dutch Ministry of Agriculture,
Nature and Food Quality and SIBEMA project,
Flanders-Bulgarian Cooperation.
(e). Red mullet (Mullus surmuletus).
Eriphia verrucosa is not a dedicated predator of
Rapana, normally preferring easier prey such as
mussels and smaller crabs. In the event of a
superinvasion, however, it is able to switch to a
diet of young Rapanas and survive. But this is
all we can expect from this crab; it is very
References
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MarBEF Newsletter
Autumn 2007
unlikely that Eriphia verrucosa will ever be able
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Dragos Micu
National Institute of Marine Research
and Development, “Grigore Antipa,”
Email: ddrraaggoossmm@yahoo.com
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SESAME:
Southern European Seas: Assessing and Modelling Ecosystem Changes
Participants on the first training course in Plankton Production, held at the Hellenic Centre for Marine Research, Greece, in July 2007.
The Integrated Project SESAME IP, launched in November 2006, is a four-year
project funded by the EC’s 6th Framework Programme. It is designed to study
the past, present and future environmental changes in the Mediterranean and
Black Sea ecosystems, and how these affect their abilities to provide goods and
services with fundamental societal importance, such as tourism, fisheries,
mitigation of climate through carbon sequestration, and ecosystem stability
through conservation of biodiversity.
SESAME unites scientists from more than 20
countries to investigate the current status of
the Mediterranean and the Black Seas. With
the help of historical data, in combination with
newly collected data, SESAME aims to identify
the environmental changes these regions have
experienced over the last 50 years. For the first
time, the two seas will be approached as a
coupled climatic/ecosystem entity. The goal is,
based on past and current status, to predict
possible changes within the next 50 years. The
project will thus provide the basis for
developing and implementing sustainable
development policies and strategies within
these regions, by involving and assisting the
relevant stakeholders, especially in a time of
strong climate change debates. SESAME’s
Figure 1. Study area for the SESAME project.
multidisciplinary approach will bring together
natural scientists and socio-economists.
Exploring the Mediterranean
and the Black Sea
Although regional data are already available,
they were, until now, hardly accessible to the
international scientific community due to
language barriers. During the first year of the
project, previously collected historical and
current multidisciplinary datasets of
physicochemical and biological parameters will
be analysed for signals of environmental
changes and trends. During the second year,
two multidisciplinary and multiship seasonal
research cruises will cover the entire
Mediterranean and Black Sea basins (see
coloured map lines for transects, Fig. 1) in
order to collect new information about the
actual status of the two ecosystems.
Ten oceanographic research vessels will
simultaneously conduct these cruises, which
are planned for March-April 2008 and for
August-September 2008. The collected highquality in situ data from all the cruises will be
used to tune and validate the basin-scale and
sub-regional models, and feed the SESAME
databases.
Data collection for model validation began at
the beginning of SESAME in the seven subregional areas, shown as shaded rectangles on
the map.
Ten 3D coupled biogeochemical-hydrodynamical models, three at basin scale
(Mediterranean, Black sea and the whole SES
area) and seven at regional scale (five subbasins and the straits – TSS and Gibraltar), as
well as a 1D model referring to carbon export,
have already been described in terms of their
structure, the basic hypotheses on which they
rely (e.g. functional/sized classes organisation
of the ecosystem) and their resolution. These
models will be used for the assessment of the
ecosystem functioning modifications that have
taken place in the last 50 years. The same
models will be used for the prediction of future
changes in the ecosystems. Particular focus has
been placed on identifying the limitations of
the models and the extension/improvement
needed to be able to address SESAME’s
objectives.
The semi-quantitative fields of economics and
social sciences will be fully addressed over five
study areas (see map). Study of these areas
will explore the possibility of transferring
and/or adapting state-of-the-art analytical
Autumn 2007
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29